The present invention relates to an automatic wheelchair brake system for preventing unwanted rearward movement of a wheelchair during an occupant's transitional ingress and egress, and more particularly to a wheelchair having a brake apparatus that automatically releases when a patient is properly seated.
Using a wheelchair enables patients suffering from various physical and mental disabilities to engage in some level of activity without experiencing the pain or limitations ordinarily placed upon them, and many patients who use wheelchairs are not permanently confined thereto. For these patients, the wheelchair is a convenient tool to facilitate mobility that is not possible otherwise. But often, getting in and out of the wheelchair can pose a problem for such users, in that the chair may roll backward unexpectedly as the patient transitions from standing to sitting, and vice versa. It is especially important that the wheelchair remains stationary during this period, since the natural motion associated with transitioning from sitting to standing, and vice versa, tends to transmit a rearward force on the wheelchair. Further, because only a minimal force is required to move the wheelchair backwards rather rapidly, the patient is extremely vulnerable to falling injuries during this transition period.
In the past, various attempts to prevent such unwanted movement involved installing a braking mechanism on the wheelchair. In fact, most wheelchairs incorporate some type of brake to stabilize the wheelchair in a stationary position by preventing rotation of the rear wheels. Conventional wheelchairs, which are foldable for storage, are invariably fitted with hand-operated brakes. These brakes engage the main drive wheels of the wheelchair, and are applied by a user (primary), or an assistant (secondary user), to stabilize the wheelchair before the primary user is seated. Once seated, the user releases the brakes by hand to again permit wheelchair mobility, and when the user wishes to leave the wheelchair, the brakes are re-applied.
Brakes of this conventional type are adequate when the user is not seriously physically handicapped and when the user is in substantial control of his mental faculties. However, when the user is severely handicapped or otherwise unable to operate the hand brake, manual brakes are quite inadequate. An unaided user who attempts to enter or exit a wheelchair that is not locked in a stationary position is faced with a difficult and dangerous task.
One of the most widely used devices for stopping and securing the wheelchair is a brake similar to that shown in U.S. Pat. No. 4,570,756 to Minnebraker et al., in which a lever arm is provided to urge a braking member into contact with the tread of the wheelchair tire. However, despite its popularity, this brake causes unnecessary tire tread wear, lacks substantial holding efficiency on sloped surfaces, and becomes almost unusable when the tire is wet. Since the device is only applied to one wheel, applying stopping action on both wheels of the wheelchair requires installation of two devices that must be engaged using two hands, which may not be an available option for a particular patient.
Similar wheelchair brakes are also disclosed in U.S. Pat. No. 3,529,700 to Marshall; U.S. Pat. No. 2,426,451 to Hammack; U.S. Pat. No. 4,384,732 to Wierwille; U.S. Pat. No. 4,852,697 to Kulik; and U.S. Pat. No. 4,350,227 to Knoche. All of these disclose braking devices for wheelchairs wherein braking pressure is applied directly to the tire rather than to the wheel rim.
Because of the above problems typically associated with prior wheelchair brakes, attempts have been made to provide an alternative brake system, which automatically remains braked while the wheelchair is unoccupied, and which releases automatically under the weight of the user when properly seated.
For example, U.S. Pat. No. 4,623,043 to Babilas discloses an automatic wheelchair brake that automatically locks both wheels when a patient attempts to rise from the wheelchair. While seated, the patient can manually operate a three-way lever brake having a manual-locked, a manual-unlocked and an automatic position. If the patient attempts to rise while the brake lever is in the manually unlocked position, the lever automatically returns to the automatic position and both wheels still lock automatically. After the patient has exited, the wheelchair may only be moved by shifting the operating lever to the manual unlock position. However, the threat of rollback remains after the wheelchair is freely repositioned, especially if an unaided patient forgets to re-engage the manual-lock before sitting, or another unaware patient attempts to sit in the unbraked wheelchair. Thus, despite the automatic engagement feature, the manual nature of this brake is not generally desirable for seriously impaired patients.
Another wheelchair having an automatically engaging braking system is disclosed in U.S. Pat. No. 3,529,700 to Marshall, and uses chains or rod linkages connected between a set of rigid actuating bars attached to the seat panel to operate a pair of transverse brake levers which engage the main wheels. U.S. Pat. No. 4,320,818 to Knoche discloses a wheelchair brake assembly for use with a conventional foldable wheelchair that provides a pair of rearwardly extending brake arms connected to adjacent side frames underneath the seat. Each brake arm includes a transverse forward portion pivoted to the side frame and has a brake shoe in biased engagement with a drive wheel. The rearward portion of each brake arm is provided with a post engageable by the wheelchair seat to pivot the brake shoe out of engagement with the wheel when the seat is depressed and moved downwardly by the weight of an occupant. The wheelchair side frames are connected by a tension spring to ensure that the brake is engaged when the wheelchair is unoccupied.
Yet another prior art wheelchair brake is the anti-rollback assembly of U.S. Pat. No. 6,092,824 to Ritchie. The one-way brake assembly is shown in FIGS. 13 and 14 as an example of a prior art wheelchair brake that automatically immobilizes the wheelchair against rearward movement when the occupant attempts to rise.
More specifically, FIG. 13 shows a wheelchair 1 having a frame 2 and an anti-rollback assembly. The anti-rollback assembly includes fastening devices 3A and 3B attached to opposing portions 2A and 2B of the frame 2 above the point where the opposing axles 4A and 4B intersect the frame 2. The fastening devices 3A and 3B include a large number of individual components as shown in FIG. 14, but the rotatable connection members 3a and 3b are most noteworthy for purposes of this discussion. A rigid crossbar 6A is rotatably attached to and interposed between the rotatable connection members 3a and 3b such that the rigid crossbar 6A transversely connects the fastening members 3A and 3B over the horizontal distance spanning between the two opposing sides 2A and 2B of the frame 2. The rigid cross bar 6A includes an arm 6B having a first portion 6a perpendicularly extending from the horizontal rigid crossbar 6A and joining with a second portion 6b at an elbow. The second portion 6b extends vertically upward from the elbow such that a third portion 6c is positioned under the wheelchair seat 7. A pair of brake arms 5A and 5B are rigidly attached to the rotatable connection members 3a and 3b and positioned to contact the rear wheels 20A and 20B such that the rear wheels are not moveable. When a patient sits on the wheelchair seat 7, the third portion 6c of the arm 6B is pressed downward, causing the rigid crossbar 6A to rotate in a rearward direction. The brake arms 5A and 5B lift upward in co-rotation with the rigid crossbar 6A and out of contact with the rear wheels 20A and 20B which are then freely moveable.
Another prior art wheelchair brake assembly is the wheelchair rollback stop of U.S. Pat. No. 6,347,688 to Hall et al. The device of Hall et al. includes a multi-part lever mechanism consisting of two levers that are attached to a wheelchair via an elongated (modified) axle bolt that acts as a fulcrum. The multi-part lever mechanism is activated (i.e., a plurality of posts with cane ends are pressed against the ground) when no patient is seated on the seat of the wheelchair, and deactivated when a patient's weight depresses the wheelchair seat. The design of the multi-part lever mechanism involves a large number of individual components that must be assembled and adjusted to ensure that the rollback stop performs properly. For example, an unmodified wheelchair (i.e., a wheelchair having a standard axle bolt) must be modified, that is, the standard axle bolt must be removed and replaced with the elongated axle bolt mentioned above. In most cases, when the wheel axle bolt is removed from the wheelchair, the wheel requires substantial bracing to avoid complete removal, due to the fact that the removed axle bolt can no longer secure the wheel to the wheelchair. In that manner, to modify a wheelchair to accommodate the rollback stop of Hall et al., replacing an existing axle bolt is no small task. Once fitted with a suitable (i.e., elongated) axle bolt, the remainder of the multi-part lever mechanism must be attached and adjusted using a plurality of pins, springs, bolts, and set-screws. Ultimately, installation is time consuming and complex.
Although automatic brakes, in general, offer advantages over manual brakes, room for improvement remains. Particularly, one problem is that the above mentioned automatic wheelchair brakes include a multitude of small parts which must be precisely adjusted to work in concert to accomplish the desired effect. Many people who are responsible for wheelchair operation and maintenance are thus hesitant to tackle such complex installation of multi-component brakes.
Portability and storage of unoccupied wheelchairs are also hindered by complex automatic brake assemblies that usually brace the frame of the wheelchair in a transverse manner. Once automatic brakes having these rigid crossbars are installed, the brakes must be at least partially uninstalled (i.e., removed) to store, transport, or otherwise collapse the unoccupied wheelchair. Given the complex nature of the multiple-component assemblies, foldable storage and transport is not easily facilitated.
Another common problem among automatic wheelchair brake mechanisms is that the safety feature itself compromises the comfort of the user. This is prevalent among automatic wheelchair brakes that involve some type of seat-activation that is directly connected to the actual brake member, such as those described above. Because applying the patient's weight to the seat activates the automatic brake to disengage, and since the brake automatically engages upon removal of that weight, the brake member beneath the seat exerts a significant upward force on the seat. Thus, patients seated in thusly equipped flexible wheelchair seats often experience discomfort or pain due to the presence of the brake activation member pushing up on the seat. Even if the amount of upward force exerted by the brake mechanism positioned immediately beneath the seat is minimal, patients' perceptions remain that the brake mechanism involves a lump of some sort on which the patient is forced to sit. This can be annoying for any patient, but can pose particularly serious problems, such as skin deterioration, for those who spend a considerable amount of time in the wheelchair.
Thus, it would be desirable to provide a wheelchair having a brake assembly that overcomes the drawbacks of the prior art. It would be particularly desirable to provide a cost effective wheelchair brake apparatus capable of automatic activation and release by an occupant, having few components to facilitate easy installation, having a nonrestrictive assembled structure to facilitate easy storage, and having a comfortable and efficient means of preventing unwanted motion of an empty wheelchair while users transition from a sitting position to a standing position, or vice versa.